Generally, rotary atomizing head type paint coating systems have been in wide use for coating vehicle bodies and the like. In connection with coating operations of by a coating system of this class, there are increasing demands for measures which can reduce the amounts of paint and solvent which have to be discarded as waste each time when changing the paint color in the course of a coating operation, as well as for measures which can cope with as many paint color changes as possible.
Noteworthy as a first prior art in this regard is Japanese Laid-Open Patent Publication No. H8-229446 which discloses a rotary atomizing head type coating system incorporating measures for reducing the amounts of waste paint and solvent and for coping with an increased number of paint colors. This rotary atomizing head type coating system employs paint cartridges of different colors which can be replaceably set in position on the system according to color specifications of a coating object such as vehicle bodies or the like. This prior art coating system is not equipped with a cleaning device for washing off residues of a previous color, and there is unable to fulfill the functions as required of the coating systems of this sort.
There have also been known the so-called automatic coating systems (e.g., as described in Japanese Laid-Open Patent Publication No. S63-175662) which are configured to perform a coating operation automatically for a vehicle body or the like according to a programmed routine. In a prior art automatic coating system of this sort, which is herein referred to as a second prior art for the convenience of explanation, a plural number of paint cartridges of different colors are located in predetermined positions within a working area of a working mechanism such as a coating robot or the like, and automatically changed from one cartridge to another at the time of a change of paint color. Further, in the case of the automatic coating system of the second prior art, in order to permit replacements of paint cartridges (changes of paint color), a hose is connected to the coating system to feed a washing fluid to a rotary atomizing head of the system. Provided internally of the coating system and in communication with the washing fluid hose is a washing fluid passage leading to the rotary atomizing head. At the time of washing off residues of a previous color from the rotary atomizing head, a washing fluid is spurted toward the rotary atomizing head through the washing fluid supply hose and passage.
Further, described in an application, which was internationally published in the WIPO gazette under WO 97/3470, is an automatic coating system which is noteworthy, for example, as a third prior art. The automatic coating system according to this third prior art includes a working mechanism which is located within a coating area, a coating machine having an atomizing unit and supported on the working mechanism, a plural number of paint cartridges which are filled with paint of different colors and interchangeably mounted on the coating system, and a cartridge changing device which functions to support and interchangeably load the paint cartridges on the coating machine.
In the case of the automatic coating system of the third prior art with the arrangements just described, a hose is connected to the coating system to feed a washing fluid to the latter in a manner similar to the above-mentioned second prior art. Provided in the coating system and in communication with the washing fluid hose is a washing fluid passage leading to a rotary atomizing head of the coating system. A washing fluid valve is provided in the washing fluid passage to open and close the same.
Thus, in the above-described coating system of either the second or third prior art, which incorporates a washing device or mechanism for a rotary atomizing head, a washing fluid supply hose is connected to a washing fluid passage which is provided internally of the coating machine. Therefore, it has inherent problems such as difficulties in handling and placing the hose in evasive positions in addition to increases in scale and weight of the coating machine itself.
Besides, in case a high voltage is applied for the purpose of enhancing the paint deposition efficiency, the high voltage could leak to the outside through the washing fluid in the washing fluid passage and the hose.